The present invention relates to plungers of the type which are used to remove liquid from a natural gas well or the like. More specifically, the invention relates to detecting position of the plunger as it moves along a length of the well.
Deep wells are used to extract gas and liquids from within the ground. For example, such wells are used to extract natural gas from underground gas pockets. The well comprises a long tube which is placed in a hole which has been drilled into the ground. When the well reaches a pocket of natural gas, the gas can be extracted to the surface.
As a natural gas well ages, liquid such as water tends to collect at the bottom of the well. This water slows, and eventually prevents, the natural gas from flowing to the surface. One technique which has been used to extend the lives of well is a plunger-based lift system which is used to remove the liquid from the bottom of the well. Position of the plunger within the well is controlled by opening and closing a valve at the top of the well. When the valve is closed, flow of gas out of the well is stopped and the plunger falls through the water to the bottom of the well. When the plunger reaches the bottom of the well, the valve can be opened whereby pressure from within the well pushes the plunger to the surface. As the plunger rises, it lifts any liquid which is above it up to the surface thereby removing most of the liquid from the well.
In order to efficiently operate the plunger, it is desirable to identify when the plunger reaches the bottom of the well. Various techniques have been used to determine when the plunger reaches the bottom of the well, for example, U.S. Pat. No. 7,963,326, issued Jun. 21, 2011, entitled “Method and Apparatus for Utilizing Pressure Signature in Conjunction with Fall Time as Indicator in Oil and Gas Wells” to Giacomino describes one technique.